1) Field of the Invention
This invention relates to an anti-fogging resin film-forming composition having a high strength in the resulting coating film and capable of protecting the surface of various materials and giving a permanent anti-fogging property to the polymer material surface.
2) Related Art Statement
Various plastic materials, glasses, transparent ceramics and mirror materials are widely used in various use fields, such as helmet shield, disaster-preventing mask, swimming goggles, mirror surface, lens of spectacles, film for agricultural house, packaging film for foods, window-glass of house, and the like, due to their excellent transparency and mirroring property. However, one of the serious drawbacks of these various materials is that, when they are used in a place kept to a high temperature and a high humidity or in a room kept to a temperature higher than that of the outdoor air, steam is condensed on the surface of these materials in the form of a fine waterdrop, and hence the surface of these materials is fogged.
In order to solve these drawbacks, various methods have been proposed. One of the methods is method (1), wherein a so-called composite film consisting of a polyester film and an anti-fogging film formed thereon or an acetyl cellulose film or the like, whose surface has previously been saponified, is stuck, for example, to a window glass of the building and house, and to a mirror in the bathroom and in the lavatory (Japanese Patent Application Publication No. 60-44,147, No. 60-44,148 and No. 60-44,149, and Japanese Patent Laid-open Specification No. 62-54,733). Further, as other methods, methods wherein a film having an anti-fogging property is formed on the surface of a transparent material. These methods are, for example, method (2), wherein a film consisting mainly of a hydrophilic polymer, such as a polymer of 2-hydroxyethyl methacrylate or polyvinyl alcohol, is formed on the surface of a transparent material (Japanese Patent Laid-open Specification No. 59-217,783 and No. 60-223,885); a method (3), wherein a film is formed on the surface of a transparent material by using a random copolymer consisting predominantly of a hydrophilic polymer segment and containing a small amount of a hydrophobic polymer segment or a combination of the hydrophilic polymer and a surfactant in order to maintain the film strength against water (Japanese Patent Application Publication No. 52-47,754); a method (4), wherein a film of a mixture consisting of a hydrophilic and hydrophobic random copolymer and a surfactant is formed on a transparent material surface (Japanese Patent Laid-open Specification No. 56-62,856 and No. 57 98,518), and the like. Further, as a concrete embodiment, there is known a method, wherein an anti-fogging coating composition is coated on the surface of a polyester film, and then the anti-fogging coating composition is cured for a short time of about 10-180 seconds. As the treating condition in this case, there are known a method (5), wherein a mixture of a coating composition, which consists mainly of a hydrophilic polymer, such as a polymer of 2-hydroxyethyl methacrylate or polyvinyl alcohol, and an ion-hardenable crosslinking agent and occasionally a surfactant, is coated on a polyester film, and the coated polyester film is heat treated to form an anti-fogging coating film on the polyester film (Japanese Patent Laid-open Specification No. 59 15,473), and a method (b), wherein a coating composition consisting mainly of a free-radical reaction-inducing polyfunctional oligomer having polyethylene oxide chains in its molecule or 2-hydroxyethyl methacrylate and containing occasionally a surfactant is coated on a polyester film, and the coated polyester film is irradiated with a radiation or an ultraviolet ray to form an anti-fogging coating film on the polyester film (Japanese Patent Laid-open Specification No. 60-156,731).
However, the above described conventional methods have the following drawbacks. In the conventional method (1), the resulting hydrophilic cellulose film is poor in water resistance, heat resistance and brittle resistance, and wrinkles and bubbles are apt to be formed in the interface between the laminated cellulose film and polyester film, and hence the laminate can not be practically used. The conventional method (2) can form a somewhat satisfactory anti-fogging coating film, but the coating film is apt to be cracked and is poor in the strength, and moreover is poor in the adhesion to the surface of a matrix to be coated and is easily peeled off from the matrix. In the conventional method (3), although the coating film has satisfactorily improved strength and adhesion, the coating film is poor in the anti-fogging property, the improvement of which property is an important object of the present invention. In the conventional method (4), although the coating film has initially a high anti fogging property, but the anti-fogging property decreases with the lapse of time, and moreover the use of the coating composition containing a large amount of the surfactant results in a coating film having low strength and adhesion, and therefore the method (4) is not still satisfactory. The conventional method (5) has a drawback that a coating film concurrently having high anti-fogging property and film strength can not be obtained due to the reason that the anti-fogging treatment of polyester film must be carried out in a short curing time. That is, the lower are the concentration of crosslinkable functional group in the hydrophilic polymer and the concentration of the crosslinking agent, the higher the anti-fogging performance of the resulting coating film is. However, in this case, the resulting coating film has not a fully crosslinked structure due to the short curing time, and hence the coating film is very poor in the strength and adhesion and can not at all be practically used. On the contrary, when the hydrophilic polymer having crosslinkable functional groups in a high concentration is used in order to obtain a coating film having a high strength, the resulting coating film is very poor in the anti-fogging property, and moreover when a surfactant is contained in the coating composition in order to develop an anti-fogging property, the resulting coating film has initially a high anti-fogging property due to the surfactant bled to surface of the coating film, but when the coating film surface is immersed in water, the surfactant bled to the coating film surface is flowed away, and further a surfactant contained in the interior of the coating film can not be bled to the film surface due to the high concentration of the crosslinking agent and hence the anti-fogging property of the coating film is low. The conventional method (6) has a drawback that, although the curing time is short, the curing reaction is apt to proceed rapidly due to the reason that the radical curing reaction is a chain reaction, and therefore the resulting coating film has a very high crosslink density and is poor in the anti-fogging property.
As described above, a satisfactory anti-fogging method for various transparent materials has not yet been found out.